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Full-Text Articles in Physics
X-Ray Scattering Study Of The Incommensurate Phase In Mg-Doped Cugeo3, Rebecca J. Christianson, Y. J. Wang, S.C. Lamarra, R. J. Birgeneau, V. Kiryukhin, T. Masuda, I. Tsukada, K. Uchinokura, B. Keimer
X-Ray Scattering Study Of The Incommensurate Phase In Mg-Doped Cugeo3, Rebecca J. Christianson, Y. J. Wang, S.C. Lamarra, R. J. Birgeneau, V. Kiryukhin, T. Masuda, I. Tsukada, K. Uchinokura, B. Keimer
Rebecca J. Christianson
We present results of a systematic x-ray scattering study of the effects of Mg doping on the high-fieldincommensurate phase of CuGeO3. Lorentzian-squared line shapes, the changing of the first-order transition tosecond order, and the destruction of long-range order with infinitesimal doping are observed, consistent withrandom-field effects in a three-dimensional XY system. Values for the soliton width in pure and lightly dopedCuGeO3 are deduced. We find that even a very small doping has a drastic effect on the shape of the latticemodulation.
Time-Dependent Strength Of Colloidal Gels, S. Manley, Benny Davidovitch, Neil R. Davies, L. Cipelletti, A. E. Bailey, Rebecca J. Christianson, U. Gasser, V. Prasad, P. N. Segre, M. P. Doherty, S. Sankaran, A. L. Jankovsky, B. Shiley, J. Bowen, J. Eggers, C. Kurta, T. Lorik, D. A. Weitz
Time-Dependent Strength Of Colloidal Gels, S. Manley, Benny Davidovitch, Neil R. Davies, L. Cipelletti, A. E. Bailey, Rebecca J. Christianson, U. Gasser, V. Prasad, P. N. Segre, M. P. Doherty, S. Sankaran, A. L. Jankovsky, B. Shiley, J. Bowen, J. Eggers, C. Kurta, T. Lorik, D. A. Weitz
Rebecca J. Christianson
Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.
Spinodal Decomposition In A Model Colloid-Polymer Mixture In Microgravity, A. E. Bailey, W. C. K. Poon, Rebecca J. Christianson, A. B. Schofield, U. Gasser, V. Prasad, S. Manley, P. N. Segre, L. Cipelletti, W. V. Meyer, M. P. Doherty, S. Sankaran, A. L. Jankovsky, W. L. Shiley, J. P. Bowen, J. C. Eggers, C. Kurta, T., Jr. Lorik, P. N. Pusey, D. A. Weitz
Spinodal Decomposition In A Model Colloid-Polymer Mixture In Microgravity, A. E. Bailey, W. C. K. Poon, Rebecca J. Christianson, A. B. Schofield, U. Gasser, V. Prasad, S. Manley, P. N. Segre, L. Cipelletti, W. V. Meyer, M. P. Doherty, S. Sankaran, A. L. Jankovsky, W. L. Shiley, J. P. Bowen, J. C. Eggers, C. Kurta, T., Jr. Lorik, P. N. Pusey, D. A. Weitz
Rebecca J. Christianson
We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time show more than 3 orders of magnitude increase in domain size, following nearly the same evolution as that in binary liquid mixtures. The late-stage growth approaches the expected linear growth rate quite slowly.
X-Ray Scattering Studies Of Two Length Scales In The Critical Fluctuations Of Cugeo3, Y. J. Wang, Y. J. Kim, Rebecca J. Christianson, S. C. Lamarra, F. C. Chou, R. J. Birgeneau
X-Ray Scattering Studies Of Two Length Scales In The Critical Fluctuations Of Cugeo3, Y. J. Wang, Y. J. Kim, Rebecca J. Christianson, S. C. Lamarra, F. C. Chou, R. J. Birgeneau
Rebecca J. Christianson
The critical fluctuations of CuGeO3 have been measured by synchrotron x-ray scattering, and two length scales are clearly observed. The ratio between the two length scales is found to be significantly different along the a axis, with the a axis along the surface normal direction. We believe that such a directional preference is a clear sign that random surface strains, especially those caused by dislocations, are the origin of the long length scale fluctuations.
Limits To Gelation In Colloidal Aggregation, S. Manley, L. Cipelletti, V. Trappe, A. E. Bailey, Rebecca J. Christianson, U. Gasser, V. Prasad, P. N. Segre, M. P. Doherty, S. Sankaran, A. L. Jankovsky, B. Shiley, J. Bowen, J. Eggers, C. Kurta, T. Lorik, D. A. Weitz
Limits To Gelation In Colloidal Aggregation, S. Manley, L. Cipelletti, V. Trappe, A. E. Bailey, Rebecca J. Christianson, U. Gasser, V. Prasad, P. N. Segre, M. P. Doherty, S. Sankaran, A. L. Jankovsky, B. Shiley, J. Bowen, J. Eggers, C. Kurta, T. Lorik, D. A. Weitz
Rebecca J. Christianson
We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.
Critical Dynamics Of A Spin-5/2 Two-Dimensional Isotropic Antiferromagnet, Rebecca J. Christianson, R. L. Leheny, R. J. Birgeneau, R. W. Erwin
Critical Dynamics Of A Spin-5/2 Two-Dimensional Isotropic Antiferromagnet, Rebecca J. Christianson, R. L. Leheny, R. J. Birgeneau, R. W. Erwin
Rebecca J. Christianson
We report a neutron-scattering study of the dynamic spin correlations in Rb2MnF4, a two-dimensional spin-5/2 antiferromagnet. By tuning an external magnetic field to the value for the spin-flop line, we reduce the effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal two-dimensional isotropic antiferromagnet. From the shape of the quasielastic peak as a function of temperature, we demonstrate dynamic scaling for this system and find a value for the dynamical exponent z. We compare these results to theoretical predictions for the dynamic behavior of the two-dimensional Heisenberg model, in which deviations from z=1 provide a measure of the …
Spin Correlations In An Isotropic Spin-5/2 Two-Dimensional Antiferromagnet, R. L. Leheny, Rebecca J. Christianson, R. J. Birgeneau, R. W. Erwin
Spin Correlations In An Isotropic Spin-5/2 Two-Dimensional Antiferromagnet, R. L. Leheny, Rebecca J. Christianson, R. J. Birgeneau, R. W. Erwin
Rebecca J. Christianson
We report a neutron scattering study of the spin correlations for the spin-5/2 two-dimensional antiferromagnet Rb2MnF4 in an external magnetic field. Choosing fields near the system’s bicritical point, we tune the effective anisotropy in the spin interaction to zero, constructing an ideal S = 5/2 Heisenberg system. The correlation length and structure factor amplitude are closely described by the semiclassical theory of Cuccoli 'et al.' over a broad temperature range, but show no indication of approaching the low-temperature renormalized classical regime of the quantum nonlinear sigma model.
Electrochemistry And Staging In La2cuo4+D, P Blakeslee, R J. Birgeneau, F C. Chou, Rebecca J. Christianson, M A. Kastner, Y S. Lee, B O. Wells
Electrochemistry And Staging In La2cuo4+D, P Blakeslee, R J. Birgeneau, F C. Chou, Rebecca J. Christianson, M A. Kastner, Y S. Lee, B O. Wells
Rebecca J. Christianson
Measurements are reported of the time dependence of the current during electrochemical oxidation and reduction at a fixed voltage of single crystals and ceramic samples of La2CuO4+d. Staging peaks in neutron measurements of the single crystals together with the electrochemical measurements and magnetization measurements confirm that stage n=6 corresponds to d=0.055 +/- 0.05, the high-d side of the oxygen-rich–oxygen-poor miscibility gap. Furthermore, stage n=4 occurs at a value of d consistent with d{n^-1. For ceramic samples it is shown that two different superconducting compounds are formed depending on the oxidation voltage used.
Analysis Of Electroluminescence Spectra Of Silicon And Gallium Arsenide P-N Junctions In Avalanche Breakdown, M Lahbabi (Adjunct), A Ahaitoufa, M. Fliyou, E. Abarkan, J.-P. Charles, A. Bath, A. Hoffmann, Sherra E. Kerns, David V. Kerns, Jr.
Analysis Of Electroluminescence Spectra Of Silicon And Gallium Arsenide P-N Junctions In Avalanche Breakdown, M Lahbabi (Adjunct), A Ahaitoufa, M. Fliyou, E. Abarkan, J.-P. Charles, A. Bath, A. Hoffmann, Sherra E. Kerns, David V. Kerns, Jr.
Sherra E. Kerns
We present a generalized study of light emission from reverse biased p–n junctions under avalanche breakdown conditions. A model is developed based on direct and indirect interband processes including self-absorption to describe measured electroluminescence spectra. This model was used to analyze experimental data for silicon (Si) and gallium arsenide p–n junctions and can be extended to several types of semiconductors regardless of their band gaps. This model can be used as a noninvasive technique for the determination of the junction depth. It has also been used to explain the observed changes of the Si p–n junction electroluminescence spectra after fast …